1. Field of the Invention
The present invention relates to a method and an apparatus for impregnating a base fiber material with a liquid resin to produce a molded article from a fiber-reinforced plastic.
2. Description of the Related Art
Fiber-reinforced plastics, which are composites made of base fibers and resins, have been known as lightweight high-strength materials. Molded articles produced from such fiber-reinforced plastics have recently been used in components for car bodies and airplanes.
Molded articles made from fiber-reinforced plastics (hereinafter referred to as molded FRP articles) can be produced, for example, by an RTM (Resin Transfer Molding) method. In the RTM method, as described in Japanese Laid-Open Patent Publication No. 2002-192535, a base fiber material is placed in a mold cavity, the mold is closed, gas in the cavity is discharged, and then a liquid resin is supplied to the cavity.
In certain cases, a molded FRP article is required to have a large thickness in excess of 10 mm, or a relatively high fiber content of about 50% by volume. If such molded FRP articles are produced using an RTM method, the base fiber material exhibits a high resistance against flow of the liquid resin. Therefore, the liquid resin may be spread insufficiently over the base fiber material, so that the base fiber material is insufficiently impregnated with the resin, thereby generating an unimpregnated area. The molded FRP article with such an unimpregnated area has insufficient strength and cannot be used as a satisfactory product.
As is clear from the above, in the RTM method, disadvantageously, it is difficult to produce a molded FRP article having a large thickness or a high fiber content with high yield.
Japanese Patent No. 4414801 proposes a technique in which liquid resin is supplied to a cavity between lower and upper molds during a process of changing the lower and upper molds from an open state to a closed state. Thereafter, gas that exists in an enclosed space formed by the lower and upper molds is vented. As described in Japanese Patent No. 4414801, according to this technique, since the cavity is placed under a negative pressure, the liquid resin can be spread in a short time and the base fiber material can readily be impregnated with the liquid resin.